This University of Pittsburgh project will determine the degradation mechanisms of current state-of-the-art thermal barrier coating (TBC) in environments comprised of particulate matter and gas mixtures which are representative of gas turbines using coal-derived synthesis gas (syngas). The observed degradation processes will be used to guide the development of improved coatings for hot section components in the potentially harsh gas turbine environments in which fuels derived from coal and even perhaps biomass are burned. The unresolved complexities associated with TBC durability include enhanced attack of yttria-stabilized zirconia (YSZ) top coating by chemical reaction, physical damage of the topcoat by molten deposit penetration, and accelerated bond coat corrosion. This work is investigating how the interaction between the ash and oxidants affect TBC degradation by using lab-scale testing. Important outcomes from this study will include understanding TBC degradation; modeling integrated gasification combined cycle (IGCC) environments to develop better coatings; and extending the service life of TBCs by mitigating degradation.

This research is using the high-temperature corrosion testing facilities at the University of Pittsburgh. The deposits currently being used are based on fly ash, and accordingly, consist of calcium oxide (CaO), aluminum oxide (Al2O3), silicon dioxide (SiO2) and iron oxides (FeOx). Additions of potassium sulfate (K2SO4) and iron sulfide (FeS) are used to simulate other ash constituents. The tests are being conducted on two different TBC system types provided by Praxair Surface Technologies (PST) of Indianapolis, Indiana. PST will also conduct thermal gradient tests for assessing TBC durability with and without deposits. Both exposed and unexposed test samples are being extensively characterized using the suite of capabilities available at the University of Pittsburgh.

Project Benefits

This project will utilize high-temperature corrosion testing facilities to determine the degradation mechanisms of current state-of-the-art thermal barrier coating (TBC) in simulated syngas environments. Turbine materials research seeks to improve coating materials that will allow for higher temperature operation and increased durability leading to increased turbine efficiency and reduced maintenance. Specifically, this project will investigate how the interaction between the ash and oxidants affect TBC degradation through enhanced attack of yttria-stabilized zirconia (YSZ) top coating by chemical reaction, physical damage of the topcoat by molten deposit penetration, and accelerated bond coat corrosion.